It has been shown that T cells from inbred A/J mice which have been suppressed with respect to the formation of a cross-reactive idiotype can passively transfer the suppression to mildly irradiated syngeneic recipients. Studies in our laboratory will be continued with the aim of ascertaining whether or not B cells as well as T cells are suppressive. Limiting dilutions of purified B cells and purified T cells will be passively transferred to determine the minimum dose required for the transfer of immunological suppression. If the number of B cells required is comparable to that of the number of T cells, then contamination by T cells can be ruled out as a cause of suppression, Also, B cells will be transferred from A/J mice, hyperimmunized against the phenylarsonate group subsequent to suppression of cross-reactive idiotype. Antiidiotypic antibody will be prepared against the new idiotypes arising in the suppressed mouse. Subsequently, B cells will be transferred from the suppressed mouse to mildly irradiated syngeneic (A/J) recipients and the latter will be immunized. We will determine whether the idiotypes of the antiarsonate antibodies arising in the recipient mice correspond to those of the donor. If so, this would be strong evidence for B cell dominance. We have shown that one can suppress 2 to 4 recipients with the spleen cells of a single hyperimmunized, suppressed donor. If the idiotype unique to the donor is transferred in substantial proportions, it should be possible to create a colony of mice possessing the idiotype of the original suppressed donor. It should be of great interest to compare the structural characteristics of antibodies of the same specificity but a variety of idiotypes from a single strain of mouse. BIBLIOGRAPHIC REFERENCES: "Competition for antigen by cell populations having receptors with the same specificity but of different idiotype", S.A. Bangasser, A.A. Kapsalis, P.J. Fraker and A. Nisonoff, Journal of Immunology, 114, 610, 1975. "Immunological suppression of idiotypic specificity", Nisonoff and S.A. Bangasser, Transplantation Reviews, 27, 100, 1975.